Add option to pass environment variables

[GuillaumeGomez]

Proposal

Add a new --env VAR=VALUE option which injects environment variables into the program, allowing them to be read by the env! and option_env! macros and from proc_macro_tracked_env.

An initial implementation (not merged) was done in rust-lang/rust#94387.

Mentors or Reviewers

@bjorn3 and @jyn514 were the ones who reviewed the original PR so at least tagging them here as potential mentors/reviewers.

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[oli-obk]

@rustbot second

[jyn514]

I want to raise a concern that this doesn't support proc-macros in practice.

[dtolnay]

Prior art: rust-lang/rfcs#2794

[jsgf]

Yeah very in favour of this, but it needs to have a way to also remove all process-environment variables, so that you can entirely specify the logical environment on the command line.

[GuillaumeGomez]

Your RFC seems more complete. Any idea why it was not approved yet?

[jsgf]

Any idea why it was [not?] approved yet?

It just needs to be driven. There are no objections, but I don't think it's got much attention. I'm happy to take it up again, esp if we have multiple independent use-cases for the functionality.

[jsgf]

I updated my impl in https://github.com/jsgf/rust/tree/env-sandbox

[apiraino]

@rustbot label -final-comment-period +major-change-accepted